The invention relates to a method for connecting a battery in a hybrid electric vehicle, which vehicle comprises a high voltage battery pack, an electric machine operable in generating and motoring modes and an internal combustion engine for driving the electric machine and/or the vehicle. More particularly the invention relates to a method for operating the electric machine that permits continued operation of the engine and electric machine as the battery pack is connected to the electrical system while the vehicle is in motion.
Generally, a hybrid electric vehicle combines electric propulsion with traditional internal combustion engine propulsion to achieve enhanced fuel economy and/or lower exhaust emissions. Electric propulsion has typically been generated through the use of batteries and electric motors. Such an electric propulsion system provides the desirable characteristics of high torque at low speeds, high efficiency, and the opportunity to regeneratively capture otherwise lost braking energy. Propulsion from an internal combustion engine provides high energy density, and enjoys an existing infrastructure and lower costs due to economies of scale. By combining the two propulsive systems with a proper control strategy, the result is a reduction in the use of each device in its less efficient range. Furthermore, in a parallel hybrid configuration, the combination of a downsized engine with an electric propulsion system into a minimal hybrid electric vehicle results in a better utilization of the engine, which improves fuel consumption. Furthermore, the electric motor and battery can compensate for reduction in the engine size.
These parallel hybrid vehicles perform various controls, for example, when the vehicle accelerates, the electric motor assists the output of the engine, and when the vehicle decelerates, the electric motor generates electric power by deceleration regeneration to charge a battery, etc. Therefore, it is possible to constantly maintain electrical energy, i.e. the remaining battery charge, in the battery and to respond to demands made by the driver on the vehicle.
In the hybrid vehicle, it is not only possible to start the engine using a starter motor dedicated for starting the engine, but also it is possible to start the engine using a driving motor for running the vehicle.
A problem with conventional hybrid vehicles, when starting the engine, is that the selection of the starter motor or the driving motor has not been appropriately performed while taking into consideration the protection of various devices and parts in the hybrid vehicles. Moreover, in the conventional hybrid vehicles, when starting the engine, the selection of the starter motor or the driving motor has not been appropriately performed in consideration of the case where drivers wish to start the engine quickly or when power from the main battery pack is not available at the time of starting.
A further problem relates to the connection of the main battery pack when the vehicle is in motion. If the main battery is not connected to the high voltage bus at start-up, or if a temporary malfunction causes the battery pack to be disconnected after start-up, then the vehicle is usually required to be stationary before a reconnection can be carried out.
In the subsequent text, the term “high voltage” is used for systems operating on voltages over 100 V, typically on 300 V or more. Similarly, the term “low voltage” is used for systems operating on voltages in the region 12-42 V.
According to a preferred embodiment, the invention relates, according to an aspect thereof, to a method for operating a hybrid electric vehicle comprising an internal combustion engine and an electrical system which electrical system comprises, an electronic control unit; an engine-driven electric machine operable as a motor for driving the vehicle or as a generator for supplying power to one or more electrical loads via a high voltage bus. A high voltage battery pack is coupled to the high voltage bus by at least one contactor arranged to connect the battery pack to the high voltage bus.
The method involves performing the steps of                detecting at least one parameter related to the state of the electrical system;        determining if the at least one parameter indicates a condition preventing the battery pack from being connected to the high voltage bus,        monitoring the condition and determining if the state of the electrical system allows the battery pack to be connected to the high voltage traction bus;        driving the electric machine as a generator using the engine,        operating the electric machine in voltage control mode during operation of the vehicle;        pre-charging the high voltage traction bus using the electric machine, and, if the condition is eliminated,        closing the at least one contactor to connect the high voltage battery pack to the traction voltage bus during operation of the vehicle.        
According to an aspect of the invention the vehicle is operated in voltage control mode from engine start, if the battery pack is prevented from being connected to the high voltage traction bus at startup. Alternatively, if the battery pack is disconnected from the high voltage traction bus during operation of the vehicle, the vehicle is operated in voltage control mode until it is detected that it is possible to reconnect the battery pack. In both cases the at least one parameter indicating a condition preventing the battery pack from being connected to the high voltage traction bus is monitored. If and when this condition is eliminated, the battery pack can be connected to the high voltage traction bus while the vehicle is being operated.
Hence, a first example involves detecting at least one parameter related to the state of the electrical system prior to operation of the vehicle and starting the engine using a starter motor if the at least one parameter indicates a condition preventing the battery pack from being connected to the high voltage traction bus. A starter motor for starting the internal combustion engine can be connected to an auxiliary battery pack. The electric machine is operated in voltage control mode using the engine until the battery pack can be connected.
A second example involves detecting at least one parameter related to the state of the electrical system during operation of the vehicle and operating the electric machine in voltage control mode using the engine if a detected parameter causes disconnection of the battery pack.
The at least one detected parameter can be that the high voltage battery has a battery temperature below a predetermined threshold, that a detected parameter is that a pre-charge resistor is inoperable, that a detected parameter is that a pre-charge circuit switch is inoperable, that a self-diagnostic test has not been completed, or that a detected parameter is that the high voltage battery is connected to a battery charger. It should be noted that these parameters do not comprise an exhaustive list of possible detectable parameters associated with a condition that can cause a malfunction in the electrical system.
The electric machine is operated in voltage control mode prior to closing the at least one contactor for pre-charging the high voltage traction bus capacitance to a desired voltage within a predetermined range of the battery pack voltage. The at least one contactor is closed to connect the high voltage battery pack to the high voltage traction bus when the voltage of the high voltage traction bus is within the predetermined range.
The invention further relates, according to an aspect thereof, to a hybrid electric vehicle comprising an internal combustion engine and an electrical system which electrical system comprises an electronic control unit. An engine-driven electric machine is operable as a motor for driving the vehicle or as a generator for supplying power to one or more electrical loads via a high voltage traction bus. A high voltage battery pack is coupled to the high voltage traction bus by at least one contactor arranged to connect the battery pack to the high voltage traction bus. The engine can be started either by the starter motor using an auxiliary, low voltage battery, or by the electric machine using the high voltage battery pack.
The electronic control unit is arranged to detect at least one parameter related to the state of the electrical system. The electronic control unit is further arranged to determine if the at least one parameter indicates a condition preventing the battery pack from being connected to the high voltage traction bus. If such a condition is detected, the electronic control unit is arranged to monitor the condition and to determine if the state of the electrical system allows the battery pack to be connected to the high voltage traction bus.
The electric machine is arranged to be driven as a generator using the engine, wherein the electric machine is arranged to be operated in voltage control mode during operation of the vehicle. The electric machine is operated in voltage control mode while the battery pack is disconnected from the high voltage traction bus. The electric machine is arranged to pre-charge the high voltage traction bus while the condition preventing the battery pack from being connected exists. The electronic control unit is arranged to close the at least one contactor to connect the high voltage battery pack to the high voltage traction bus during operation of the vehicle, if it is determined that the condition is eliminated.
As indicated above, the vehicle is operated in voltage control mode from engine start, if the battery pack is prevented from being connected to the high voltage traction bus at start-up, or if the battery pack is disconnected from the high voltage traction bus during operation of the vehicle.
According to a first example, the electronic control unit is arranged to start the engine by means of a starter motor if the at least one parameter indicates a condition preventing the battery pack from being connected to the high voltage traction bus is determined prior to operation of the vehicle, that is, before or during an engine start-up sequence. A starter motor can be connected to an auxiliary battery pack for starting the engine.
According to a second example the electronic control unit is arranged to detect at least one parameter related to the state of the electrical system during operation of the vehicle and the engine is arranged to operate the electric machine in voltage control mode if the battery pack is disconnected from the high voltage traction bus while the vehicle is being operated.
The electric machine is arranged to be operated in voltage control mode to pre-charge the high voltage traction bus capacitance to a desired voltage within a predetermined range of the battery pack voltage. Following the pre-charge, the at least one contactor is arranged to close to connect the high voltage battery pack to the high voltage traction bus when the voltage of the high voltage traction bus is within the predetermined range.
The at least on detected parameter can be that the high voltage battery has a battery temperature below a predetermined threshold, that a detected parameter is that a pre-charge resistor is inoperable, that a detected parameter is that a pre-charge circuit switch is inoperable, or that a detected parameter is that the high voltage battery is connected to a battery charger.
The present invention also relates to a computer program, computer program product and a storage medium for a computer all to be used with a computer for executing the method as described in any one of the above examples.